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Ukraine Fights Advancing Russian Forces

Western allies have announced sweeping new sanctions against Moscow as a defiant President Volodymyr Zelenskiy said Ukrainian forces were repelling Russian troops advancing on Kyiv.

Seeking to ratchet up economic punishment for Russian President Vladimir Putin over his invasion of Ukraine, the US and its European partners said they would kick key Russian banks off the main global payments system.

As fighting continues across Ukraine, the Western nations also said they would impose restrictions on Russia's central bank to limit its ability to support the rouble and finance Putin's war effort.

Meanwhile huge explosions lit up the predawn sky south of Kyiv early on Sunday.

President Volodymyr Zelenskyy's office said one of the blasts was near the Zhuliany airport, and the mayor of Vasylkiv, about 40km south of the capital, said an oil depot there was hit.

"We have withstood and are successfully repelling enemy attacks. The fighting goes on," Zelenskiy said in a video message from the streets of Kyiv posted on his social media.

The capital and other cities have been pounded by Russian artillery and cruise missiles.

The United Nations says it has confirmed at least 240 civilian casualties, including at least 64 people killed, in the fighting.

Terrified men, women and children sought safety inside and underground, and the government maintained a 39-hour curfew to keep people off the streets.

Putin launched what he called a special military operation on Thursday, ignoring weeks of Western warnings and saying the "neo-Nazis" ruling Ukraine threatened Russia's security - a charge Kyiv and Western governments say is baseless propaganda.

A US defence official said Ukraine's forces were putting up "very determined resistance" to the three-pronged Russian advance that has sent hundreds of thousands of Ukrainians fleeing westwards, clogging major highways and railway lines.

"As Russian forces unleash their assault on Kyiv and other Ukrainian cities, we are resolved to continue imposing costs on Russia that will further isolate Russia from the international financial system and our economies," the Western allies said as they escalated their punitive response.

"We will implement these measures within the coming days," a joint statement from the United States, France, Canada, Italy, Great Britain and the European Commission said.

The move - which the French finance minister had earlier called a "financial nuclear weapon" because of the damage it would inflict on the Russian economy - deals a blow to Russia's trade and makes it harder for its companies to do business.

SWIFT, or the Society for Worldwide Interbank Financial Telecommunication, is a secure messaging network that facilitates rapid cross-border payments, making it a crucial mechanism for international trade.

The Kremlin said its troops were advancing again "in all directions" after Putin ordered a pause on Friday. Ukraine's government said there had been no pause.

While NATO has said it will not deploy troops to Ukraine, a string of countries are sending military aid.

US President Joe Biden approved the release of up to $US350 million ($A484 million) worth of weapons from US stocks, while Germany, in a shift from its long-standing policy of not exporting weapons to war zones, said it would send anti-tank weapons and surface-to-air missiles.

EU foreign policy chief Josep Borrell said the bloc's foreign ministers would meet on Sunday evening to discuss emergency assistance for Ukraine's armed forces.

Amid a barrage of cyberattacks blamed on Moscow, Ukrainian Vice Prime Minister Mykhailo Fedorov said his government will create an "IT army" to fight back.

Fedorov also called on Saturday on SpaceX billionaire Elon Musk to provide Ukraine with the company's Starlink satellite broadband service.

Musk responded on Twitter: "Starlink service is now active in Ukraine. More terminals en route."

A Ukrainian presidential adviser said about 3500 Russian soldiers had been killed or wounded and that Russian troops had not made serious gains on the third day of fighting.

Western officials have also said intelligence showed Russia suffering higher casualties than expected and its advance slowing.

Russia has not released casualty figures and it was impossible to verify tolls or the precise picture on the ground.

AAP with The Project